<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>border属性讲解</title>
    <style>
        .border{
            width: 200px;
            height: 200px;

            /* 按照三要素来编写 */
            /* border: 5px solid lightgreen; */
            /* 上下 左右 */
            border-width: 4px 10px;
            /* 上 右 下 左 */
            border-style: solid dotted dotted dashed;
            border-color: green yellow blue red;

            /* 按照方向来编写border */
            border-top-color: black;
        }
        input{
            /* 清除默认样式 */
            border: 0;
            outline: none;
        }
        .username{
            width: 200px;
            height: 18px;
            border: 1px solid lightgreen;
            padding-left: 20px;
        }
        .username:hover{
            border: 3px solid yellow;
        }
    </style>
</head>
<body>
    <!-- 三要素 粗细 样式 颜色 -->
    <!-- <div class="border"></div> -->

    <input type="text" class="username">
</body>
</html>